Tim has $39$ pairs of headphones and $13$ music players. Tim wants to sell all of the headphones and music players in identical packages. What is the greatest number of packages Tim can make?
Explanation: In order to know how many packages Tim can make, we need a number that is a factor of ${39}$ and ${13}$, so that the ${39}$ pairs of headphones and the ${13}$ music players can be divided up evenly. To find the greatest number of identical packages, we want to find the greatest common factor of ${39}$ and ${13}$. To do so, let's find factors of ${39}$ and ${13}$. ${39}$ : $1, 3, {13}, 39$ ${13}$ : $1, {13}$ The greatest common factor of ${39}$ and ${13}$ is ${13}$. In math notation this looks like: $ \text{gcf}({39}, {13}) = {13}$. The greatest number of identical packages that Tim can make is ${13}$.